1. Field of the Invention
The present invention relates to a film coating nozzle for applying coating material to a surface of a product such as a compressor piston, used in an arrangement which requires wear resistance and liquidtightness, and thereby forming film on the surface of the product, and an apparatus and a method for coating a compressor piston using the same. More particularly, the present invention relates to a film coating nozzle which can spread, by a dispenser method, applied coating material to form film of a uniform film thickness, and an apparatus and a method for coating a compressor piston using the same, which can coat the compressor piston through a series of continuous processes.
2. Description of the Related Art
Generally, a product such as a compressor piston used in an arrangement requiring wear resistance and liquidtightness is coated on its surface with film of a predetermined thickness. This coating technique has already been employed in various industrial fields. As well known in the art, in this coating technique, it is important that the thickness be uniform over the entire surface of the applied film. Specifically, while, for example, a Teflon coating is applied to a circumferential outer surface of a head part of the compressor piston, upon coating the compressor piston, a thickness and uniformity of a coated film greatly influence the performance of a compressor, and therefore should be carefully controlled.
As coating methods for improving wear resistance and liquidtightness of a compressor piston, powder coating, spraying or electrostatic painting are well known in the art. However, these coating methods suffer from disadvantages in that variance in thickness of coated film is substantial. In particular, in a spray coating method, since a coating process is involved and sprayed coating material spatters, regions which do not require application of coating material are also coated with coating material and thus, coating material is excessively wasted. Further, in the spray coating method, a surrounding environment is polluted by coating material which spatters during a coating procedure.
To cope with these problems occurring in the conventional spray coating method, coating apparatuses are disclosed in Japanese Patent Laid-open Publication No. Heisei 8-173893 and International Patent Application No. PCT/JP00/00096. Each of the coating apparatuses has a rotation support device which rotatably supports a cylindrical product to be coated, a coating material injecting device which is installed above the rotation support device in such a way as to be moved upward and downward and has a nozzle for applying coating material to a circumferential outer surface of the product rotated by the rotation support device, and a blade which spreads to a uniform film thickness coating material applied to the circumferential outer surface of the product by the coating material injecting device in such a way as to remove excess coating material.
However, the conventional coating apparatuses still encounter problems in that, since the blade for removing excess coating material applied to the circumferential outer surface of the cylindrical product must be installed separately from the nozzle at a position adjoining the rotating cylindrical product, a construction of each coating apparatus as a whole is complex. Moreover, because driving and controlling of the blade serving as a coating material spreading device is complicated, maintenance and repair costs and time of the coating apparatus are increased.
Furthermore, in the conventional coating apparatuses, while it is possible to apply coating material, for example, to a circumferential outer surface of a head part of a compressor piston, it is impossible to apply coating material to a bridge part of a piston for a fixed displacement swash plate type compressor or wing parts of a piston for a variable displacement swash plate type compressor. For this reason, in the conventional art, a coating process for the bridge part or wing parts should be performed by a spraying method, in a state wherein the piston which is coated with coating material on its circumferential outer surface is moved to another place or apparatus. Hence, by the fact that two different methods are employed, operation control for the entire coating apparatus is made further complicated. Also, inherent problems of the spray coating method, which are related with increase in coating material consumption and pollution of surrounding devices due to spatter of coating material, still exist.